The invention will be described in relation to Xenograft bioprostheses (ie: implant materials obtained from animals) for the replacement or repair of damaged human tendons and ligaments, but, it is to be understood that the invention is not limited thereto as the implantable materials of the invention may be used for other purposes such as patches for hernia repair and as intermediate-life sutures.
For some years, collagen-based animal or human tissues have been used as bioprostheses such as heart valves, blood vessels, ligaments and pericardium. These tissues have been treated with aldehydes such as glutaraldehyde to minimize their rejection potential (ie: antigenicity).
Australian Patent Specification 497,462 discloses a non-antigenic, non-thrombogenic, infection-resistant graft derived from the human umbilical cord. To provide such a graft, the Wharton's jelly (which surrounds the vein and the two arteries of the umbilical cord) is removed manually or by flushing with a saline solution. A mandrel is then inserted into the vein and the vein and the arteries are dissected our of the umbilical cord itself. The vein and arteries are then subjected to a tanning treatment with an aldehyde to stiffen the material. Glutaraldehyde is noted as being the preferred tanning agent from the stand points of elimination of any traces of antigenicity and thrombogenicity as well as convenience.
The vascular prostheses disclosed in Australian Patent Specification 516,741 consists of a coherent tubular wall of non-human collagenous tissue which has been subjected to glutaraldehyde tanning so as to provide cross-linked collagen fibres and a tubular reinforcement of fibre mesh embedded within the coherent wall of tanned collagenous tissue.
The tanning step is carried out in a bath of buffered glutaraldehyde and upon its completion all free glutaraldehyde is removed by washing in baths of saline and hydrogen peroxide. The buffered glutaraldehyde has a glutaraldehyde strength of 5% and the pH of the bath is held at about 7.4 by using sodium phosphate or potassium acid phosphate.
According to Australian Patent Specification 516,741 the desirable features of the ovine reinforced collagen conduit revolves around the glutaraldehyde treatment which alters the antigen combining sites to shield the Xenograft from immune reaction.
The vascular prostheses disclosed in Australian Patent Specification 64,816/80 is produced by subjecting a length of animal ureter to glutaraldehyde tanning. The ureter as discussed in the specification includes those from humans, oxen, cows, sheep, goats, pigs, donkeys, camels, deer and kangaroos. Tanning is carried out in a buffered glutaraldehyde bath having a glutaraldehyde strength of 2.5% by weight.
The modified bioprostheses disclosed in Australian Patent Specification 87,332/82 consists of a tissue specimen to which is bonded a mesh material so that the bioprostheses can be placed with at least a portion of the mesh against a living tissue surface to enable the living tissue to grow into the mesh. More specifically, that specification discloses the use of glutaraldehyde treated mammalian tendons but does not deal with the glutaraldehyde treatment itself.
Collagen is a protein which is the major fibrous component of skin, bone, tendon, cartilage, ligaments and blood vessels. Collagen is rich in glycine and also contains proline, hydroxyproline, lysine and hydroxylysine. As indicated above, glutaraldehyde is used to cross-link the amino acid side chains of the collagen, mainly lysine, to improve the strength of the collagen fibre, but, in so doing, much of its natural flexibility is lost and its ability to be resorbed by the body is also greatly reduced.
Thus, the aldehyde-fixed collagen which has improved mechanical strength and antigenicity does not lend itself to use as a Xenograft bioprostheses for the replacement or repair of damaged human tendons and ligaments because of its reduced flexibility and its inability to be resorbed. As a consequence, there is little replacement of the graft by host tissue with suitable properties.
At the present time, there is no satisfactory ligament or tendon substitute although many synthetic and biological materials have been tried. The most commonly used substitute is autogenous material (for example, patella tendon) but this is not always available or of adequate strength. There is, therefore, a need for a tendon or ligament substitute which possesses appropriate fineness, length, flexibility, strength and the ability to be replaced by endogenous tissue with desirable characteristics.
It is an object of this invention to provide human implantable collagen-based materials with desirable properties with respect to antigenicity and possessing mechanical strength and flexibility which will largely be replaced by endogenous tissue with suitable characteristics so as to be useable to repair or replace tendons and ligaments as well as for other purposes.